1. Field of the Invention
The invention relates to an apparatus for measuring flow vectors in gas currents.
2. Description of Related Art
U.S. Pat. No. 3,941,744 discloses an optical device in which a light beam emitted from a light source is divided into two partial beams, each of which is focused in the measuring volume. Solid particles contained in the flow and traversing a focusing point, flash up, and said flash up is detected by an analyzer. If the flow vector of a particle is in alignment with a straight line traversing both focusing points, a start pulse is produced at the first focusing point and a stop pulse at the second focusing point. From the time interval between said pulses, the flow rate, i.e. the vector amount, may be detected. The measuring expenditure involved with said two focus-processes is quite time-consuming. Only such flow vector components which are situated in a plane extending vertically to the optical axis of the system may be measured. Said plane must be determined by a series of measurements. The component extending in parallel to the optical axis cannot be determined.
British patent No. 2,109,548 describes a further development of the stated double-focus process. According to said British patent, it is also possible to measure a flow vector component extending in parallel to the optical axis of the system so that the flow vectors may be determined completely as to amount and direction. In this process, called the three-component process, a multicolored laser beam is split into two components of different colors. Each of said components is split up into two partial beams which are polarized vertically to each other. Thus, there are formed four partial beams in total of which two always intersect in the measuring volume and form a focusing point. One focusing point is situated on the optical axis of the system. By turning an image rotating prism, the position of the other focusing point may be easily changed. In order to evaluate the flashes produced by the flowing particles, the radiation of said flashes is selected, depending on polarization and color, in order to generate the start and stop pulses.
Due to the beam splitting, to the subsequent out-reflection out of the incident radiation of the radiation components emerging from the measuring volume, and to the need for ensuring a spatial separation of the beam components, the known devices require much space. These measuring instruments, being of extensive volume, may not be used under restricted room conditions.
It is an object of the invention to provide a device for measuring flow vectors in gas currents that may be used in restricted space conditions and for which the measuring setup is simple and more easily controllable.